21
Notes on using the Calibrated
616
Hickok part number 20877-1
The
calibration
tube
is
intended
to
be
used
as
a
tool
to
compare and adjust
the
final overall accuracy
of
any
539C
tester against a factory standard
539C
tester
in
order
that
your
tester
will give comparable results
to
the factory
standard and comply
with
the
roll chart results.
It
should be noted
that
this value
is
not necessarily
the
actual
"book value" transconductance
of
the
tube
measured on precision test equipment accordingto
tube
manufacturer's standard procedures but a representation
of
the
transconductance
that
a factory calibrated
Hickok
539C
should measure.
Even
though
the
mutual conductance calibration tests performed
with
the
simulated
test
circuit show
the
correct
read ings,
other
factors and irregula rities
will
noticeably affect
the
fina I readings. Power supply loading, small
imbalances
in
screen voltage, plate voltage, mismatches between
the
two
halves
of
the
83 and
5Y3
rectifiers,
resistorvalues and
other
things all add
upto
affect
the
readings.
Even
using the
wrong
type
of
fuse lamp
can
substantially change
the
calibration
of
the
tester.
The
tube
is
not
intended
to
be
used
to
adjust
out
significant problems
orfaults
in
the
operation
of
the
539C.
It
is
only
to
be
used
to
match
the
reading
of
a properly
functioningtesterto
that
oft
he
factory standard.
If
significant
errors in operating voltages are found at
the
time
of
calibration,
first
determine
that
the
rectifier tubes are
working properly and have substantially equal
output
from
each half
of
the
tube. A good test
is
to
substitute
known good
re
placement rectifier tubes a
nd
see
if
the
problem resolves. Replacement
of
a rectifier tube
will
always require areca libration
of
the
teste
r.
Verify
that
all
of
the
test
voltages are correct a
nd
that
the
fixed
resistor values have
not
shifted
with
age
or
by electrical damage.
It should
be
noted
that
even
ca
lib ratio n by this method
will
never guara ntee perfect accuracy. A different
calibration
tube
will
seldom read
the
exact calibration value on any given 539 calibrated
with
another tube. They
will
be
very close but
the
tester
is
simply
not
capable
of
that
kind
of
repeatable accuracy
from
sample
to
sample.
Slight differences
in
component tolerances, calibration tubes and mostly
the
lack
of
regulation
of
operating
voltages due
to
loading.
meter
reading inaccuracy and
the
coarse adjustment capability
of
the
line adjust control
will
cause a discrepancy
in
test
results.
While Hickok designed the
539C
to
be
a
better
than average
tube
tester
it
is
still not a laboratory grade
instrument.
Some deviation
from
perfect accuracy must
be
expected.
The
calibration
tube
is
carefully tested and
specified
for
use
with
the
Hickok
539C
only. Because
other
Hickok model testers and
other
manufacturers testers
use
different voltages
for
testing than
the
539C
they
may, but more likely
will
not, read
the
same value
of
mutual
conductance
for
the
calibration tube. Only a perfect
tube
would
test
out
to
the
same mutual conductance value
for
every tester and every set
of
ope rating voltages applied
to
it.
Since
there
is
no perfect
tube
this should
not
be
expected.
Never place
the
tube
in emission type teste
rs
or
testers
of
other
bra
nds
because
of
the
possibility
of
perma nent
changes in calibration value. Because
it
was specifically calibrated
for
the
539C
circuit using
539C
operating
conditions its value
for
checking othe r testers using
different
test conditions
is
margina I at best
31
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